This invention relates to an automatic controlling and tracking system of the direction of a directive repeating antenna of a television repeating system, and more particularly to an automatic controlling and tracking system of the direction of a directive repeating antenna mounted on an aircraft which is used to send video signals photographed by an air-born television camera to a ground office.
Where television video signals are sent to a ground office from an aircraft in flight it is required to control the directive repeating antenna on the aircraft such that the antenna is always directed to the ground station. One difficult problem encountered in the control of the direction of the repeating antenna is that the coordinate of the ground office is determined by the longitude and the latitude of the globe whereas the aircraft coordinate that determines the direction of the repeating antenna is independent from the latitude and longitude of the globe (globe coordinate) accordingly, in order to automatically direct the air-borne repeating antenna to a definite direction toward the ground office it is necessary to determine the correlationship between the globe coordinate and the aircraft coordinate and to control the direction of the repeating antenna based on the correlationship so as to always cancel the variations in the coordinate caused by the motion of the aircraft.
According to one method of controlling the direction of the air-borne repeating antenna in a manner just described, the rolling and pitching angles of the craft detected by a vertical gyroscope mounted on the craft and the azimuth angle of the craft detected by an orientation gyroscope are used, because the relationship between the globe coordinate and the craft coordinate can be determined by the rolling angle, pitching angle and the orientation angle. For this reason, a stabilized platform which is automatically controlled so that the rolling and pitching angles are made to be always zero is mounted on the craft, such stabilized platform being used to realize the globe coordinate on the craft. By providing proper means for adjusting the orientation angle to a preset angle that indicates the desired ground office for the stabilized platform, it is possible to maintain the repeating antenna in a direction toward the desired ground office.
However, with such an automatic direction control system utilizing the stabilized platform on the aircraft, it is necessary to provide three control systems for the orientation angle, rolling angle and pitch angle for the purpose of controlling the attitude and orientation of the stabilized platform. However, in order to provide three degrees of freedom for the driving mechanism of the stabilized platform it is necessary to use a gimbal support having two degrees of freedom necessary to control at least the rolling angle and the pitching angle in the same manner as a vertical gyroscope. Accordingly, it is necessary to provide for one gimbal a driving mechanism for the other gimbal. In addition, it is necessary to use a plurality of slip rings and brushes for establishing electric circuits. Moreover, it is necessary to mount these gimbal mechanisms for supporting the repeating antenna on the outside of the craft so that the direction of the electric wave radiated by the repeating antenna will not be disturbed by the movement of the craft.
Accordingly, according to the commercial repeating system utilizing an air-borne repeating antenna it has been the practice to project a non-directive repeating antenna to the outside of the craft or to control only the horizontal position of the non-directive antenna by using above described stabilized platform. However, since the repeating antenna is non-directive, the repeating area is more limited than a case using a directive repeating antenna, for example, to an area within a circle having a radius of about 20 Km from the ground office. However, such system is disadvantageous in that the size of the control apparatus is bulky and complicated.
In the automatic direction control system of an air-borne repeating antenna, it is necessary to provide a ground control system for the ground office that tracks the movement of the aircraft and controls the direction of the receiving antenna in accordance with the movement of the aircraft. As such ground system for performing such tracking and reception it has been used a control system that controls the direction of the receiving antenna such that it is maintained in a direction giving the maximum receiving field intensity. However, in order to effectively receive the electric wave radiated by a non-directive repeating antenna it is necessary to use a large receiving antenna in order to obtain sufficiently large receiving field in intensity.